Metal pickling process



252. COMPOSITIONS,

Patented June 5, 1934 UNITED STATES 1,961,652 PATENT OFFICE Rubber Service Laboratories Company,

Akron,

Ohio, a corporation of Ohio No Drawing. ApplicatiohSeptembenlS,1931,

Serial No. 563,673 r 20 Claims.

The present invention relates to the art of cleaning metallic surfaces, and particularly to a new inhibitor, which is added to a pickling bath to prevent undue attack upon the surface of a metal when subjected to a pickling process by immersion in a liquid of an acid nature.

More particularly certain objects of the present invention are to obviate over-pickling, embrittlement and pitting of the articles treated; to minimize the amount of metal lost in pickling; to prolong the effective life of the pickling bath; and particularly to facilitate and increase the efficiency of the pickling operation. Other and further objects of the invention will be apparent from the following description and accompanying examples.

In the art of pickling, the metal is treated with a dilute acid to remove oxides such as rust, scale and other deposits, after which the metal is preferably washed with water and dipped into an alkaline bath to remove the last traces of free acid. The acid removes the rust and scale, but unfortunately, from the pickling standpoint, unless some agent to prevent such action is present, it attacks the cleaned metal itself, thereby causing loss of metal and producing an evolution of hydrogen gas, which escapes into the air, carrying with it a fine spray of the acid liquor from the pickling bath and producing an atmosphere possessing corrosive properties and one which is injurious to health and damaging to equipment.

By the present invention, these objectionable features of the pickling process are substantially overcome or reduced to a This is accomplished by adding to the pickling bath a regulating agent or inhibitor, which acts to restrain the acid from attacking clean metal, but assists in removing the rust, scale and other deposits, or, in other words, the regulator or inhibitor causes the acid selectively to remove such materials without appreciably attacking the clean portions of the metal under treatment.

In the examples hereinafter set forth for carrying out the metal pickling process, conditions were imposed which duplicated, so far as possible, those commonly followed in commercial practice, so far as concerned acid concentrations and temperatures employed.

It is known that reaction products of ammonia, an aldehyde and carbon bisulfide, for example, carbothialdines, are regulators or inhibitors when employed in a metal pickling bath. It has now been found, however, that more efficient inhibitors are obtained when the said reaction products are rearranged or transformed preferably by heat-treating in the manner hereinafter described. The preferred new class of inhibitors, as disclosed in the present application, comprises such a rearranged and preferably heat-treated (Cl. 14e s reaction product of ammonia, an aldehyde and carbon bisulfide.

One method whereby one of the preferred class of compounds, for example, heat-treated carbothialdine, was prepared follows:

The 'carbothialdine, prepared by the action of carbon bisuliide upon acetaldehyde-ammonia in the presence of ethyl alcohol (cf. Beilsteins Handbuch der organischen Chemie, 3d ed., Vol. I, p. 919), was heated with a volatile solvent, for example, ethyl alcohol, from which it was precipitated, to a refluxing temperature and maintained at that temperature until the heat transformation was completed. The solvent used and any water present in the solution thus formed were removed by any suitable means, as for example by distillation. The dried residual product was a brittle resin at ordinary temperatures.

The value of the above product as an inhibitor was determined in the following manner: A steel test piece, substantially 3 x 4 in dimension, cut from 30 gauge hot rolled tin plate stock, exposing approximately 24 square inches of surface and weighing 17.108 grams was immersed for 40 minutes in 750 c. c. of a water solution of sulfuric acid, containing approximately 6% by weight of 66 B. acid, to which had been added 0.047 grams of the inhibitor above described. The temperature of this bath was maintained at 80 to 85 C. After being pickled in the manner described, the test piece was again weighed, and the weight found to be 17.095 grams, showing a loss of only 0.013 grams, or 0.00054 grams per square inch of surface exposed. A similar test piece weighing 18.499 grams and treated in the same manner, but without the use of any inhibitor, lost 0.519 grams, or 0.02163 grams per square inch of surface exposed. Thus it is shown that when carbothialdine, heat-treated in the manner described, is employed as an inhibitor, the loss in weight per square inch of surface exposed is only 2.5 per cent as great as results if no inhibitor is employed in the pickling process. A greater saving in metal losses results from the use of a larger amount of inhibitor than that employed in the example. Moreover, the steel plates pickled in the presence of the inhibitor set forth are clean and not stained upon removal from the pickle bath.

Other heat-treated reaction products of ammonia, an aldehyde and carbon bisulfide have been prepared and employed as inhibitors in the pickling process. Thus, the following compounds have been prepared and tested as inhibitors in the manner hereinbefore described:

Compound A.Product obtained by reacting substantially one molecular proportion of ammonia with substantially one molecular proportion of butylaldehyde in the presence of a suitable solvent, for example,ethyl alcohol, further treating the solution thus formed with substantially one-half a molecular proportion of carbon bisulfide, and heating the resulting mixture at a refluxing temperature until the heat transformation of the reaction product was completed. The solvents present, such as alcohol and water, were removed by any convenient means, as for example by distillation, and any impurities present, such as ammonium thiocyanate, were, if desired, removed by extraction with a suitable solvent such as water.

Compound B.Product obtained by reacting ammonia with crotonaldehyde, further reacting with carbon bisulfide and heating the product thus formed in a manner analogous to that described for the preparation of Compound A.

Compound C.Product obtained by reacting ammonia with aldol, further reacting with carbon bisulfide and heating the product thus formed in a manner analogous to that described for the preparation of Compound A.

Compound D.-Product obtained by reacting ammonia with formaldehyde, further reacting with carbon bisulfide and heating the product thus formed in a manner analogous to that described for the preparation of Compound A, except that in this case the aldehyde was used in the form of a substantially 35% aqueous solution.

Compound E.Product obtained by treating substantially one-half a molecular proportion of carbon bisulfide with substantially one molecular proportion of heptaldehyde in the presence of a suitable solvent, for example, ethyl alcohol, reacting the resulting solution with substantially one molecular proportion of ammonia, and heating the mixture thus formed in a manner analogous to that described above for the preparation of Compound A.

Compound F.Product obtained by treating substantially one-half a molecular proportion of carbon bisulfide with substantially one molecular proportion of benzaldehyde, reacting the resulting solution with substantially one molecular proportion of ammonia, and heat-treating the product thus formed in a manner analogous to that described above for the preparation of Compound E.

The results of the tests obtained on immersing steel test strips of 30 gauge hot rolled tin plate stock, 3" x 4" in dimension for 40 minutes in 750 cc. of a water solution containing 6% by weight of 66 B. sulfuric acid at to C., in the presence of the indicated quantity of one of the above described inhibitors, are given in Table I.

Weight Weight of Weight of Weight of 5 r Inhibiting compound inhibitor steel strip steel strip g employed embefore after g 0! ployed pickling pickling Surface exposed Grams Grams Grams Gram Compound A 0. 047 16. 462 16. 451 0. 00046 Compound 13 0. 047 16. 776 16. 761 0. 00063 Compound 0. 047 16. 977 16. 958 0. 00079 Compound D-.. O. 047 16.786 16. 775 0. 00046 Compound 0. 047 16. 632 16.620 0. 00050 Compound F--. 0. 047 16. 706 16.684 0.00092 None None. 18. 499 17. 980 0. 02163 It is apparent from the data set forth that the preferred class of materials constitutes an important and highly efficacious group of inhibitors, as in all cases wherein one of the preferred inhibiting compounds was incorporated in the pickle liquor there resulted a great saving in the loss in weight of the steel test strips as compared with that resulting when no inhibitor was employed.

As a further example of the preferred class of inhibitors, a product was prepared by reacting ammonia with furfural, further reacting with carbon bisulfide and heating the product thus formed in a manner analogous to that described above for the preparation of Compound A. The compound thus prepared was tested in the manner hereinbefore described and found to possess the inhibiting qualities of the preferred class of compounds.

Other examples of this preferred class of inhibitors may be prepared by reacting other aldehydes than those hereinbefore set forth with ammonia and carbon bisulfide and heat-treating the resulting products in a manner analogous to that described above. Thus, propylaldehyde, valeraldehyde, isobutyl-acetaldehyde, acrolein, cumic aldehyde, phenylacetaldehyde, cinnamyl aldehyde, naphthaldehydes, and the like, may be so reacted, and the resulting products employed as inhibitors in the manner above described.

Other modes of employing inhibitors of the class hereinbefore set forth in the acid pickling of metals are apparent to those skilled in the art to which this invention pertains. The products described additionally may be employed in the presence of foaming agents, ionizable substances or other materials ordinarily used. Again, other acids than sulfuric acid may be employed in the pickle bath. Thus hydrochloric acid, as well as other inorganic acids, may be employed in the pickle bath in conjunction with the preferred class of inhibitors in the manner hereinbefore set forth.

What is claimed is:

1. A process of pickling a metal which comprises subjecting the metal to be pickled to the action of a mineral acid solution containing a small proportion of a rearranged reaction product of an aldehyde, ammonia and carbon bisulfide produced by heat-treatment thereof below the temperature of boiling water.

2. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a sulfuric acid solution containing a small proportion of a rearranged reaction product of an aliphatic aldehyde, ammonia and carbon bisulfide produced by heattreatment thereof below the temperature of boiling water.

3. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a sulfuric acid solution containing a small proportion of a rearranged reaction product of acetaldehyde, ammonia and carbon bisulfide produced by heat-treatment thereof below the temperature of boiling water.

4. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a sulfuric acid solution containing a small proportion of a reaction product of an aldehyde, ammonia and carbon bisulfide, which had been rearranged by heat-treatment in the presence of a volatile organic solvent below the temperature of boiling water.

5. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a sulfuric acid solution containing a small proportion of a reaction product of acetaldehyde, ammonia and carbon bisulfide, which had been rearranged by heat treatment in the presvvlIll vul I IVI'U ence of a volatile organic solvent below the temperature of boiling water.

6. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a sulfuric acid solution containing a small proportion of a rearranged carbothialdine produced by heat-treating said material at a temperature below the boiling point of water in the presence of ethyl alcohol.

7. A pickling bath for metal products which comprises a mineral acid solution containing a small proportion of a rearranged reaction product of an aldehyde, ammonia and carbon bisulflde produced by heat-treatment thereof below the temperature of boiling water.

8. A pickling bath for iron and steel products which comprises a sulfuric acid solution containing a small proportion of a rearranged reaction product of an aliphatic aldehyde, ammonia and carbon bisulfide produced by heat-treatment thereof below the temperature of boiling water.

9. A pickling bath for iron and steel products which comprises a sulfuric acid solution containing a small proportion of a rearranged reaction product of acetaldehyde, ammonia and carbon bisulfide produced by heat-treatment thereof below the temperature of boiling water.

10. A pickling bath for iron and steel products which comprises a sulfuric acid solution containing a small proportion of a reaction product of an aldehyde, ammonia and carbon bisulfide, which had been rearranged by heat-treating said reaction product at a temperature below the boiling point of water in the presence of a volatile organic solvent.

11. A pickling bath for iron and steel products which comprises a sulfuric acid solution containing a small proportion of a reaction product of acetaldehyde, ammonia and carbon bisulfide, which had been rearranged by heat-treating said reaction product at a temperature below the boiling point of water in the presence of a volatile organic solvent.

12. A pickling bath for iron and steel products which comprises a sulfuric acid solution containing a small proportion of a rearranged carbothialdine produced by heat-treating said material at a temperature below the boiling point of water in the presence of ethyl alcohol.

13. A process of pickling iron and steel products, which comprises subjecting the metal to be pickled to the action of a sulfuric acid solution containing a small proportion of a rearranged carbothialdine produced by heating said material below the boiling point of water.

14. A pickling bath for iron and steel products which comprises a sulfuric acid solution containing a small proportion of a rearranged carbothialdine produced by heating said material below the boiling point of water.

15. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of an acid solution containing a small proportion of a reaction product of an aldehyde, ammonia and carbon bisulfide heattreated in the presence of an aliphatic alcohol at a temperature below the boiling point of water.

16. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a sulfuric acid solution containing a small proportion of a reaction product of acetaldehyde, ammonia and carbon bisulfide heat-treated in the presence of an aliphatic alcohol at a temperature below the boiling point of water.

17. A process of pickling iron and steel products which comprises subjecting the metal to be pickled to the action of a sulfuric acid solution containing a small proportion of a material formed by heat-treating carbothialdine in the presence of ethyl alcohol below the boiling point of water.

18. A pickling bath for iron and steel products which comprises an acid solution containing a small proportion of a reaction product of an aldehyde, ammonia and carbon bisulfide heat-treated in the presence of an aliphatic alcohol at a temperature below the boiling point of water.

19. A pickling bath for iron and steel products which comprises a sulfuric acid solution containing a small proportion of a reaction product of acetaldehyde, ammonia and carbon bisulfide heat-treated in the presence of an aliphatic alcohol at a temperature below the boiling point of water.

20. A pickling bath for iron and steel products which comprises a sulfuric acid solution containing a small proportion of a material formed by heat-treating carbothialdine in the presence of ethyl alcohol below the boiling point of water.

DEAL H. TOMPKINS. 

